ASP.NET MVC Ajax Form: Is enctype correct? Why doesn't file get uploaded?

In the case that the user doesn't have Javascript activated, in order to draw a form, I begin this way:

<% using (Html.BeginForm("Create", "Language", FormMethod.Post,
     new {enctype="multipart/form-data"}))
 { %>
 

If the user has Javascript activated, the following code is used:

<% using (Ajax.BeginForm("Create", "Language",
     new AjaxOptions { UpdateTargetId = "CommonArea" },
     new { enctype = "multipart/form-data" }))
 { %>
 

The problem is this:

In the first case, I can get the file uploaded using the following instruction in the business layer:

// Get the uploaded file
 HttpPostedFile Flag = HttpContext.Current.Request.Files["Flag"];
 

In the second case, this instruction doesn't work. How do I know upload that file using the Ajax.BeginForm? Is the code right? Can anyone more experience advise about using jQuery plug-in to upload file before the form submission?

Thank you

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